This invention relates to electro-optical devices whose electromagnetic radiation absorption characteristics can be selectively altered by influence of a suitably controlled electric field. More particularly, this invention is directed to a sandwich type cell in which two layers of electrochromic material are separated by solid, semi-solid or liquid ion conducting media and which has a means to illuminate the imaging area.
In commonly assigned, copending U.S. applications, Ser. No. 41,153, Ser. No. 41,154, and Ser. No. 41,155, all filed May 25, 1970, and U.S. Pat. No. 3,521,941 and 3,578,843; Ser. No. 41,153, abandoned and refiled as Ser. No. 211,857, Dec. 23, 1971, abandoned and refiled as Ser. No. 361,760, May 18, 1973, now U.S Pat. No. 3,879,108; Ser. No. 41,154 abandoned and refiled Apr. 13, 1972, now pending; Ser. No. 41,155, now U.S. Pat. No. 3,708,220; there are described electro-optical devices exhibiting a phenomenon known as persistent electrochromism wherein electromagnetic radiation absorption characteristic of a persistent electrochromic material is altered under the influence of an electric field. Such devices were employed in sandwich arrangement between two electrodes. Coloration was induced by charging the electrochromic film negative with respect to the counter-electrode, employing an external potential. The counter-electrode can be the same as the persistent electrochromic material or different.
By reversing the original polarity of the field or by applying a new field, it was also possible to cancel, erase or bleach the visible coloration.
These steps of color inductionand erasure are defined as cycling.
Although the devices described in the prior applications are effective to change their electromagnetic radiation transmitting properties under the influence of an electric field, and have extremely good visibility over a wide range of lighting conditions, including high ambient light, they operate by light absorbtion and are therefore not viewable in the dark.
It is therefore an object of this invention to provide an electrochromic imaging device viewable in darkness.
A further object is to provide an electrochromic device having means for illuminating the display area.
These and other objects of the invention will become apparent as the description thereof proceeds.